1. Field of the Invention
The present invention relates generally to a height control system for an automotive suspension system for adjusting or regulating vehicular height within a predetermined height range. More specifically, the invention relates to a vehicular height control system which can vary a target height, about which the predetermined height range is defined, so that frequency of height adjustment during vehicular travel on an undulated road.
2. Description of the Background Art
In the recent years, there have been developed various vehicular height control systems for regulating height of a vehicle body relative to road surface and whereby for regulating vehicular attitude. In the typical construction of prior proposed vehicular height control system, vehicular height is monitored by a vehicle height sensor which monitors height of the vehicle body relative to the road surface or to a suspension member rotatably supporting a road wheel. Height adjustment is performed by adjusting suspension force to be exerted between the vehicle body and the suspension member to maintain the vehicular height within a predetermined height range. In practice, the suspension force is generated by means of a pressure chamber which is connected to a pressurized fluid source to introduce thereinto and discharge therefrom a pressurized working fluid, such as air, viscous oil and so forth.
Some of the prior proposed height control systems employs variable target height for varying the vehicle height range toward which the vehicle height is adjusted, depending upon the vehicle driving condition. For example, one of the vehicular height control system employing the variable target height has been disclosed in the Japanese patent First (unexamined) publication (Tokkai) Showa 61-263818. In the disclosed system, two target heights are employed. One of the target height is used for detecting the vehicular height requiring the height adjustment for starting height adjustment. The other target height is used for detecting the timing for termination of the height adjustment.
In the prior proposed height control systems, detects are encountered when the vehicle enters into an undulated road from smooth road for temporarily stopping. Because the undulation of the road surface tends to cause variation of the relative distance between the vehicle body and the road wheel to vary the vehicular height out of the predetermined height range. If vehicle starts to run immediately after temporary stop at the undulated road, height adjustment may not be required despite of the fact that the vehicular height as monitored is out of the predetermined height range. However, the prior proposed height control system is responsive to the vehicular height out of the predetermined height range to perform height adjustment to adapt the vehicular height at the undulated road. This requires another height adjustment when the vehicle starts to run again on the smooth road.
Furthermore, when the vehicle travels on the undulated road repeating temporary stop, height adjustment is too frequency performed to exhaust a compressor as a fluid pressure source and to degrade riding comfort.